Generally, pavements and bases for highways may be divided into the broad classifications of "flexible" and "rigid". The term "rigid" is usually applied to those structures or constructions which consist of Portland cement concrete, in that the concrete possesses considerable flexural strength which enables it to act as a beam.
The term "flexible" as applied to a pavement structure embraces substantially all other types which include as primary components a wearing surface layer, a base layer and a subgrade layer. With this type of a pavement structure, distortions occurring in the subgrade or base layers are reflected in each of the other layers and the tendency is for all layers of the structure to conform to the same shape under loading.
With either type of roadway, the subgrade and base are of fundamental importance in the construction of adequate roadways since they support the pavement load and the prior art has made efforts to overcome defects associated therewith. Primary among the problems of roadways are those associated with frosting and pumping with pumping being of particular importance in connection with concrete pavement roadways.
Frost action results in very severe damage to bases and subgrades of both the rigid and flexible type of pavements and is occasioned by the existence of freezing temperatures in those areas. In many instances the pore water of the base or subgrade is supplemented, after freezing, by the attraction thereto of additional water through means of capillary forces as well as seepage, and the resulting expansion in volume upon complete freezing of the water induces a severe roadway upheaval. Prior art preventive measures for this destructive action have, among other things, included the removal of soils which are particularly subject to frost action and the replacement thereof with granular materials to the frost line depth or greater. Such prior art attempts have been found to be costly and frequently ineffective especially in the presence of relatively shallow water tables.
Pumping and/or subgrade failure is evidenced in connection with concrete pavements by spalling primarily at joints in turn resulting in the ejection from the joints and formed cracks of water, subgrade soil and mud, and ultimately complete breaking of the roadway structure takes place. The formation of cracks in the pavement also permits seepage of surface waters to the subgrade resulting in the further erosion thereof and finally deteriorating the subgrade to the point where it is incapable of sustaining the required traffic loads, thereby causing further breaking-up of the roadway and/or pavement. The prior art has attempted to inhibit such subgrade deterioration, resulting in the breaking-up of the roadway pavement, trying to seal all cracks as they occur and, in the case of severe deterioration, to drill holes in the road and thereafter force suitable materials in slurry form through the holes to the subgrade in order to fill the openings between the subgrade and pavement bottom. This constant maintenance problem is highly undesirable and wasteful in that it only prolongs for a short period the time within which the roadway must be completely replaced.
The prior art, as shown by U.S. Pat. No. 2,737,092, has also attempted to overcome such roadway problems by providing plywood encased or embedded in rubber and placing such as to be sandwiched directly between the bottom side of the concrete pavement and the top side of the supporting earth subgrade as well as placing such as to be sandwiched directly between the respective sides of the concrete pavement and the respective juxtaposed sides of the earth adjacent the concrete pavement. By expanding upper disposed portions of the rubber, it was hoped that moisture would not enter as between the concrete pavement and the adjacent rubber-encased plywood. Such, as well as other prior art attempts to solve the problems of weather-induced roadway deterioration have not proven to be either successful or acceptable.
The invention as herein disclosed and described is primarily directed to the minimization if not solution of the aforestated as well as other related and attendant problems of the prior art roadway structures.